In the field of vehicle engines, ways are constantly being sought, in the interest of the environment, to minimize the emissions that occur. Exhaust gas treatment alone is no longer sufficient for the demands now being made; the emergence of low-boiling fuel components from the fuel tank also needs to be prevented if at all possible. Sealed tank venting devices in which the fuel vapors emerging from the fuel tank are conveyed, via a venting line, to an adsorption filter have therefore been introduced. Since the activated carbon of the filter possesses only limited storage capability, the filter must be flushed with ambient air and the fuel vapors must be conveyed to the engine for combustion. The fuel vapors must be conveyed in defined quantities.
In carbureted engines or gasoline engines with intake duct injection, the fuel vapor is delivered by way of the vacuum produced in the intake duct of the carburetor. This method is not possible to the desired extent, however, in direct-injection engines, which yield considerable fuel saving. But there are difficulties with turbocharged gasoline engines as well, since in significant portions of the characteristics diagram the pressure in the intake duct is positive with respect to the atmosphere. Ways have therefore been sought to improve the flushing mass flow.
German Unexamined Application 196 39 116 discloses a tank venting device for motor vehicles in which an air delivery pump is used for the regeneration quantity. A device of this kind is independent of the vacuum in the intake duct of the engine. The air delivery pump is operated at variable rotation speed as a metering pump. It can also be used as a diagnosis pump in order to detect leaks. A device of this kind is relatively sluggish, however, since there is a long delay in the pump's reaction to changes in engine output.